Mechanical tuning devices for magnetron tubes and the like physically alter the resonant structure of the tube. In most cases known in the art a bellows or diaphragm structure is provided in the vacuum-enclosing envelope of the tube and through it linear motion is provided to the tuning mechanism from outside the envelope. Bellows are always potentially the vacuum failure mode in a magnetron tuner, particularly where rapid tuning is required.
In another type of tuning mechanism, sometimes called a "Spin-Tuned" magnetron, a rotatable operator outside the envelope is magnetically coupled through the envelope to rotate a tuning cylinder inside the envelope; this mechanism provides random tuning with the resonance frequency being altered according to a sinusoidal function. A specific frequency of oscillation, or a specific tuning profile, cannot be pre-set with the Spin-Tuned mechanism. Moreover, the operator moves the magnetic lines of force with respect to the portion of the envelope which is placed between the driving and driven elements, inducing currents in that portion of the envelope which create opposite magnetic poles. The introduction of a magnetic material between the driving and driven elements in that operating configuration would shunt the lines of force and impair the operation of the device.
It is the object of this invention to provide a means to rapidly tune a resonant-cavity electron tube, such as a magnetron, to a specific frequency, or to program a specific profile of frequencies, without resorting to the use of bellows or diaphragms.
It is another object of the invention to provide an operator for such tuning means having a driving element outside the vacuum-enclosing envelope of the tube and a driven element inside the envelope with a portion of the envelope between them in which no induced current is set up in said portion of the envelope. More particularly, it is an object of the invention to provide such an operator which places its magnetic lines of force at a fixed position relative to the said portion of the envelope.
A further object of the invention is to provide such an operator in which magnetic material can be incorporated into said portion of the envelope between the driving and driven elements without risk of cutting lines of magnetic force between said elements, and which can be operated with minimum power.